In the decontamination of infectious waste, namely medical waste, it is important to insure that the ultimate waste product, which is to be discarded, is free of pathogenic microorganisms. It is also highly desirable, and in some instances required by law, to render infectious waste in a condition such that individual components, such as disposable syringes, bandages, body fluid receptacles, and even body parts removed in surgery or in autopsies, are unrecognizable.
Infectious waste such as medical waste is generated by hospitals, medical laboratories, and the like and is required to be decontaminated prior to being disposed. Examples of medical waste include hypodermic syringes, glassware, slides, gauze, needles, infectious tissues, blood-soaked materials, red bag waste, or other such potentially infected or contaminated medical waste materials typically generated during the normal operation of a hospital, medical laboratory, or the like. Public concern over the proper treatment and disposal of medical waste products has increased over the past several years. This increase is due in part to an increased public awareness of the diseases that can be transmitted by biologically contaminated waste products. It is therefore desirable to produce a disposal system which adequately disinfects infectious waste products while rendering the waste unrecognizable to the degree that it can be disposed of in an approved disposal facility and/or used as a fuel source without posing further infection threats due to contact with the post-treated residual waste.
The prior art has attempted to address the problem of disposing of medical waste by methods such as specialized and filling, incineration, steam autoclaving, chemical treatment, and/or radiation treatment. Environmental regulations have severely limited the use of incineration for infectious waste disposal due to the potential production of gaseous emissions that may contain high levels of toxic heavy metals, e.g. cadmium, chromium, lead, mercury, dioxins and furans generated by the plastics and metallic content derived from syringes, needles, and sharps included in the waste. In addition, incinerators are not fully satisfactory because they require regular servicing and cleaning.
Steam decontamination is another known method for treating medical waste. Steam decontamination is primary performed in steam autoclaves. Steam autoclaving is a thermal process in which the wastes are disinfected by exposure to high-temperature steam and pressure. The high temperature and good penetrability of steam effectively destroys the infectious agents. Since the waste is rendered disinfected, it can be directly landfilled. However, for steam autoclaving to be an effective treatment method, the steam must fully penetrate the waste to ensure that all infectious microorganisms are destroyed. Also, since autoclaved waste is neither mechanically destroyed nor significantly reduced in volume, it is still recognizable as medical waste and treated hypodermic needles still pose a stick threat.
Still another method is the chemical decontamination of infectious waste. Hospitals and other health care facilities have used chemical agents routinely for decades in the decontamination of infectious waste. As in steam autoclaving, chemical decontamination will not be effective unless there is adequate contact between the infectious waste and the chemical. In addition, the chemical should be maintained at a sufficient concentration and there should be sufficient exposure time between the waste and chemical to achieve proper levels of decontamination. There are several other disadvantages of using chemicals in the decontamination of infectious waste including potential occupational exposures of workers to chemical concentrations in the air and through skin contact; the possibility of toxic byproducts in the wastewater; chemical hazards involved with the use and storage of the chemicals; chemical residue in the treated waste; and offensive odors.
Still another method of disinfecting infectious wastes is to use radiation treatment. The radiation may be microwave frequencies, shortwave radiofrequencies, and the like. The radiation treatment suffers from several disadvantages. First, radiation treatment by itself will not render the waste unrecognizable. Second, radiation involving the use of microwaves is not suitable for treating chemotherapy wastes or human organs or body parts. Third, the infectious waste must have a significant moisture content to insure effective treatment with microwaves.
A more promising approach for decontaminating medical waste is to use a thermal friction extruder apparatus using friction generated by counter-rotating interleaved worm gear augers or screws to grind and heat the waste. The basic concept of using counter-rotating screws to impart heat-generating friction to a material is disclosed, for example, in U.S. Pat. No. 4,599,002, which issued on Jul. 8, 1986 (hereinafter, “the '002 patent”). This patent specifically discloses a screw extruder for compressing a material in which two interleaved counter rotating screw or auger members extend through a plurality of casing members, each separated by a corresponding one of a plurality of throttle plate members. The throttle plate members each has an orifice there through of a preselected dimension that is selected to effectively block the free-section of the screw members whereby, material to be compressed is pressed against the throttle plate member with a large force thereby causing heat that creates pulverization and drying of the material by friction on each of the throttle plate members. However, the '002 patent apparatus is not designed to decontaminate infectious waste and would not be able to generate enough heat to do so without some kind of modifications.
International Patent Application No. PCT/US2011/042905, which was published on Jan. 5, 2012 as International Publication Number WO 2012/003507 A1 (hereinafter, “the 507 application”) discloses a system which employs a thermal friction extruder apparatus similar in construction to the extruder disclosed in the '002 patent, to decontaminate infections waste. To increase the amount of heat generated in the extruder, an adjustable outlet size extruder die is located at the terminal end of the apparatus for converting the ground medical waste into an extrudate and controlling the backpressure of the extrudate as it exits the extruder. The extruder die has an adjustable outlet valve piston disposed therein for controlling the size of and therefore the temperature of the extrudate. The extruder die can thus be employed arguably to impart enough heat to the waste that it will be decontaminated.
However, in practice, to insure that the amount of heat generated by the extruder is sufficient to raise the temperature of the waste high enough to disinfect the same, it has been found that the size of the extruder die has to be adjusted so small, that it becomes too difficult to move the material through the extruder die. In addition, the tremendous backpressure imparted to the material stream by the extruder die subjects the apparatus to excessive wear and tear.